Logging while drilling (LWD) generally refers to the measurement of land formation properties during the excavation of a wellbore or other hole through the use of tools integrated into the drilling device. LWD systems are typically a part of the bottom hole assembly, which is the lower portion of a drill string that provides force for the drill bit to break soil. LWD systems deliver real-time measurements for updating reservoir models and avoiding drilling problems. The timely data that LWD systems provide can guide well placement so that a wellbore remains within the most productive portion of a reservoir. With the benefits that LWD systems provide, drilling to extended reach reservoirs and horizontal wells becomes easier, especially in highly variable shale reservoirs.
Electromagnetic (EM) LWD systems use EM waves to measure the land formation properties around a drilling device. Typically, EM LWD systems consists of at least one transmitter and at least one receiver. The transmitter excites an EM field in the formation around the system that is subsequently measured by the receiver. The received measurements are useful for evaluating formation parameters, such as resistivity, permeability, and distance to a boundary. Continuing development of the oil industry leads to increasing numbers of horizontal wells being drilled. The drilling of horizontal wells requires the real-time detection of formation boundaries ahead of and around the drilling device. EM LWD systems are capable of providing this real-time detection, but currently available EM LWD systems do not have the efficiency and accuracy required to meet industry expectations.